In many industrial and commercial locations it is desirable to supply electrical power from a ceiling rather than from a wall or floor, primarily because arrangements can more easily be changed along the ceiling to accommodate changing location requirements for appliances, instruments or other work machines in the space. Ceiling power supply systems which are particularly intended to accommodate changing conditions include cable reels and sliding contact devices with pendant cords and connectors.
The circumstances which give rise to the need for such a system can be more fully appreciated by considering a manufacturing or food preparation space in which tables with instruments or appliances are arranged in a specific way for a specific product. Power cables or cords can be arranged to depend from junction boxes or other devices attached to the ceiling so that each instrument is connectable to a cord which arrives at the location of the instrument from almost directly above. This is the proper arrangement for various safety and efficiency reasons. It is quite dangerous to have power cords draped across adjacent appliances or instruments because a cord can tip or damage an instrument and also because an appliance involving heating elements can damage a cord. If a new product requires rearrangement of the tables and instruments, the power cords must also be moved, preferably without the need for basic rewiring in the ceiling, particularly where the wiring involves solid conduit. Thus, devices have been developed to try to keep the cords substantially vertical. These includes bus duct arrangements with numerous connecting points as well as cable reels.
However, such devices are not usable in spaces in which cleanliness is a paramount consideration because they inevitably have places which accumulate dirt and from which the dirt can fall into the space when any part of the apparatus is moved. In addition, they are not suitable for use with a suspended ceiling which is desirable, and in some cases essential, for appearance as well as cleanliness. Food service facilities and industrial clean rooms used for the manufacture of items such as semiconductor devices are examples of spaces which have these requirements.